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Acoustic relaxation theory for visco-elastic media provides for sound propagation in unconsolidated marine sediments. For the frequency range of 14 to 200 kHz, dispersion for compressional-wave and shear-wave velocity is negligible for all practical purposes, but sound absorption shows significant changes. (Author).
The phenomenon of sound transmissions through marine sediments is of extreme interest to both the United States civilian and Navy research communities. Both communities have conducted research within the field of this phenomenon approaching it from different perspectives. The academic research community has approached it as a technique for studying sedimentary and crustal structures of the ocean basins. The Navy research community has approached it as an additional variable in the predictability of sound trans mission through oceanic waters. In order to join these diverse talents, with the principal aim of bringing into sharp focus the state-of-the-science in the problems relating to the behavior of sound in marine sediments, the Office of Naval Research organized and sponsored an invited symposium on this subject. The papers published in this volume are the results of this symposium and mark the frontiers in the state-of-the-art. The symposia series were based on five research areas identified by ONR as being particularly suitable for critical review and for the appraisal of future research trends. These areas include: 1. Physics of Sound in Marine Sediments, 2. Physical and Engineering Properties of Deep-Sea Sediments, 3. The Role of Bottom Currents in Sea Floor Geological Processes, 4. Nephelometry and the Optical Properties of the Ocean I'laters, S. Natural Gases in Marine Sediments and Their Mode of Distribution. These five areas also form some of the research priorities of the ONR program in Marine Geology and Geophysics.
As part of its continuing program to stimulate superior basic research in the marine environment, the Office of Naval Research, Ocean Science and Technology Division, sponsored a series of closed seminar-workshops in 1972-1973. Each seminar focused upon one re search area of marine geology which is relatively new and in need of a critical evaluation and accelerated support. The subjects areas chosen for the seminars were: 1. natural gases in marine sediments and their mode of distribution, 2. nephelometry and the optical properties of ocean waters, 3. physical and engineering properties of deep-sea sediments, and 4. physics of sound in marine sediments. The objectives of each seminar-workshop were to bring into sharper focus the state-of-the-science within each subject area, to effect some degree of coordination among the investigators working within each of these areas and to provide the Ocean Science and Technology Division guidance for national program support. This volume.contains most of the papers presented at the semi nar on the physical and engineering properties of deep-sea sediments. The seminar was held at Airlie House, Airlie, Virginia on April 24- 27, 1973 and was organized and chaired by A. Inderbitzen. The at tendees were invited from among the leading investigators in this field from both the engineering and scientific disciplines. Each attendee was requested to prepare a paper within his area of spe ciality.
In July 1972, the U.S. Office of Naval Research identified several areas that it interpreted as being of interest to the U.S. Navy. Four of these research areas were then selected for their special importance in understanding physical processes on the ocean floor. In some of these, a great wealth of data has accumulated over the past two or three decades, but controversy exists in the interpretation of the results. In others, new techniques have re cently been devised that could lead to the collection and synthesis of new information. There was yet a third area in which little study had been undertaken and the results available appeared of great potential importance. The latter subject constitutes the title of this volume. To assess the information available and to facilitate plans for further research in the fields of interest that had been identified, the U.S. Office of Naval Research sponsored four symposia. The first was held in November 1972 at the University of California Con ference Center, Lake Arrowhead. The title of the symposium was "Natural Gases in Marine Sediments and Their Mode of Distribution". Twenty lectures were presented over a three-day period. All but two participants at this symposium subsequently submitted papers, which are published in this volume. In addition, Dr. K.O. Emery, who did not attend the symposium, supplied a manuscript on a topic most re levant to the subject matter discussed.
In situ measurements of compressional (sound) velocity and attenuation were made in the sea floor off San Diego in water depths between 4 and 1100 m; frequencies were between 3.5 and 100 kHz. Sediment types ranged from coarse sand to clayey silt. These measurements, and others from the literature, allowed analyses of the relationship between attenuation and frequency, relationships between attenuation and other physical properties, and study of appropriate viscoelastic models which can be applied to saturated sediments. Some conclusions are discussed. (Author).